A constitutive theory for the mechanical response of amorphous metals at high temperatures spanning the glass transition temperature : application to microscale thermoplastic forming of Zr₄₁.₂Ti₁₃.₈Cu₁₂.₅Ni₁₀Be₂₂.₅

Abstract

Bulk metallic glasses (BMGs) are a promising emerging engineering material distinguished by their unique mechanical properties and amorphous microstructure. In recent years, an extremely promising microscale processing method for bulk metallic glasses, called thermoplasticforming has emerged. As with any emerging technology, the scientific basis for this process is at present fragmented and limited. As a result their is no generally agreed upon theory to model the large-deformation, elastic-visco-plastic response of amorphous metals in the temperature range relevant to thermoplastic-forming. What is needed is a unified constitutive framework that is capable of capturing the transition from a elastic-visco-plastic solid-like response below the glass transition to a Newtonian fluid-like response above the glass transition. We have developed a finite-deformation constitutive theory aimed to fill this need. The material parameters appearing in the theory have been determined to reproduce the experimentally measured stress-strain response of Zr₄₁.₂Ti₁₃.₈Cu₁₂.₅Ni₁₀Be₂₂.₅ (Vitreloy-1) in a strain rate range of [10-5, 10-1] s-1, and in a temperature range [593, 683] K, which spans the glass transition temperature [nu]9 = 623K of this material. We have implemented our theory in the finite element program ABAQUS/Explicit. The numerical simulation capability of the theory is demonstrated with simulations of micron-scale hot-embossing processes for the manufacture of micro-patterned surfaces.